Self-Learning
There are thousands of people learning JavaScript and web development in the hopes of getting a job. Often, self-learning leaves gaps in people’s understanding of the JavaScript language itself.
It’s actually surprising how little of the language is needed to make complex web pages. People making entire sites on their own often don’t have a good grasp of the fundamentals of JavaScript.
It’s rather easy to avoid the complex topics and implement features using basic skills. It’s also easy to create a website by relying on Stack Overflow without understanding the code being copied.
If you’re looking to master JavaScript interviews, check out Step Up Your JS: A Comprehensive Guide to Intermediate JavaScript
Interviews
The problem is that questions testing your understanding of JS are exactly what many tech companies ask in their interviews. It becomes clear very quickly when an applicant knows just enough to have scraped by, but doesn’t have a solid understanding the language.
Here are concepts that are frequently asked about in web development interviews. This is assuming you already know the basics such as loops, functions, and callbacks.
Concepts
- Value vs. Reference — Understand how objects, arrays, and functions are copied and passed into functions. Know that the reference is what's being copied. Understand that primitives are copied and passed by copying the value.
- Scope — Understand the difference between global scope, function scope, and block scope. Understand which variables are available where. Know how the JavaScript engine performs a variable lookup.
- Hoisting — Understand that variable and function declarations are hoisted to the top of their available scope. Understand that function expressions are not hoisted.
- Closures — Know that a function retains access to the scope that it was created in. Know what this lets us do, such as data hiding, memoization, and dynamic function generation.
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this— Know the rules ofthisbinding. Know how it works, know how to figure out what it will be equal to in a function, and know why it’s useful. -
new— Know how it relates to object oriented programming. Know what happens to a function called withnew. Understand how the object generated by usingnewinherits from the function’sprototypeproperty. -
apply,call,bind— Know how each of these functions work. Know how to use them. Know what they do tothis. -
Prototypes & Inheritance — Understand that inheritance in JavaScript works through the
[[Prototype]]chain. Understand how to set up inheritance through functions and objects and hownewhelps us implement it. Know what the__proto__andprototypeproperties are and what they do. - Asynchronous JS — Understand the event loop. Understand how the browser deals with user input, web requests, and events in general. Know how to recognize and correctly implement asynchronous code. Understand how JavaScript is both asynchronous and single-threaded.
- Higher Order Functions — Understand that functions are first-class objects in JavaScript and what that means. Know that returning a function from another function is perfectly legal. Understand the techniques that closures and higher order functions allow us to use.
More Resources
If the links included aren’t enough, there are countless resources out there to help you learn these concepts.
I personally created Step Up Your JS: A Comprehensive Guide to Intermediate JavaScript to help developers advance their knowledge. It covers all of these concepts and many more.
Here are resources which I’ve read or watched at least some of and can recommend.
Good luck on your interviews.
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Feel free to check out some of my recent work.
Step Up Your JS: A Comprehensive Guide to Intermediate JavaScript
What I learned from attending a coding bootcamp and teaching another one
Latest comments (23)
Great stuff!
I can share that in coding-academy.org we fearlessly teach those 10 concepts in great depth, as they are most frequently asked in job interviews!
How about Promises?
Great Post, will read all the links.
Thanks for this piece! I've added this to me "Learn Next" list and plan to go through a lot of the links you've shared. I already checked the "hoisting" one and it cleared up a lot of things that have confused me in the past.
"Understand that objects, arrays, and functions are copied and passed by reference."
If something is passed by reference it is NOT copied. That's the whole point of passing by reference. May want to change the wording there.
That's the point. Arrays & objects are not copied when they're assigned, either using
=or passed into a function. Only the reference is copied/passed in.YDKJS books are essential for anyone that is trying to get into front-end basics.
Great article. Thank you for this!
Thank you! This deserves a unicorn!
With the advent of the
classkeyword in ES6, is it still necessary to understandprototypeand friends?Unfortunately yes, even with the nicer syntax it's still plain old prototype chain. They missed the historical opportunity to clean up this mess.
The class keyword is just different syntax for creating objects. Once the object is created it still uses the same prototypal inheritance objects always have.
Using the 'class' keyword without understanding prototypal inheritance is like building a house with no understanding of carpentry. Eventually something's going to break, and you won't know how to fix it.
Absolutely. The class keyword uses prototypes in its implementation. It's just "syntactic sugar", or a simpler way of using prototypes, but we're still using prototypes nonetheless. It's key to the core of OOP in JS.
I think it is, because, in the background, class still uses prototype chain etc. You might understand some things better (or debug faster) if you understand how it really works.
For someone wanting to move away from just using JS as a way to add functionality to a basic webpage, and start using it for the complex ecosystem that it has become, this article helps immensely. Thank you!